The present invention concerns a one-piece mounting rim for a tire with a radial carcass, which together with a tire tread support ring and the said tire, forms a rolling assembly that is particularly useful in the case of rolling at an inflation pressure abnormally low compared with the recommended pressure, such that the said service pressure may even become zero. The invention also concerns the said assembly.
With a view to overcoming the above difficulties, patent EP 0 673 324 describes a rolling assembly consisting of a tire and comprising a one-piece wheel rim with two rim seats said to be inclined outwards and extended axially towards the outside by two protrusions or humps of small height. The seat of the rim edge that is to be on the outside of the vehicle is extended axially inwards by a bearing surface designed and adapted to receive a tread support, while the seat towards the inside of the vehicle is extended axially inwards by a rim flange connected to the bearing surface via a mounting groove. The preferred variant of the said rim has two seats inclined outwards and of unequal diameter, the seat generally located on the outside of the vehicle having a diameter smaller than the diameter of the seat located towards the inside of the vehicle.
The diameter difference between the two seats may make it unnecessary to have the mounting groove near the second rim seat with the larger diameter, the axially internal end of the said second rim seat being connected to the bearing surface of the tread bearing support by a rib of small or zero height. The assembly""s bearing support, which is a support made of an elastomer material that can undergo deformation to an oval shape and can be fitted onto the bearing surface, can have an axial width equal to the axial distance between the two tire beads. The said tread bearing support, as its name implies, serves to prevent the collapse of the tread and so allows the tire to roll with an acceptable degree of deflection despite the deficit or absence of inflation gas, while keeping the outer tire bead firmly in position on its rim seat.
A rolling assembly as described above comprises a tire tread bearing support and indeed must comprise such a support, on pain of not having available a safety element which is essential during rolling in what is called the degraded condition, i.e. when the tire""s inflation pressure becomes low or zero.
To avoid the accidental mounting and use of such a rolling assembly without a tread bearing support, the invention proposes a rim corn rising two rim seats with different diameters inclined towards the outside and extended axially outwards by two humps of small height, the rim seat of smaller diameter being joined axially inwards to a bearing surface via a truncated conical portion and the rim seat of larger diameter being joined axially on the inside to the said bearing surface by a rib of small or zero height, whose axially interior wall has a generatrix which makes, relative to the rotation axis, an angle open radially and axially towards the outside equal to at most 30xc2x0, characterized in that the said rib, which has an axially interior wall of axial width at most equal to the axial width of the said second seat, is provided circumferentially with at least two transverse grooves of small size.
A seat xe2x80x9cinclined outwardsxe2x80x9d is understood to be a seat whose axially inside edge is a circle of larger diameter than the circle of the axially outer edge. Similarly, the diameter of a rim seat is the diameter of its edge having the largest diameter. A hump xe2x80x9cof small heightxe2x80x9d, bearing in mind the dimensions of the rims concerned and the sizes of the tires to be fitted on the said rims, is understood to mean a hump whose height is at most 2.5% of the minimum diameter of the rim""s bearing surface. Likewise, a rib of small height is one whose height is at most equal to 2.5% of the minimum diameter of the rim""s bearing surface.
Due to the combined presence of the slope and the grooves formed in the truncated conical portion disposed between the bearing surface of the tread bearing support and the axially internal end of the rim seat, the above wheel rim does not allow the primary airtightness required for the tire to be inflated, unless the tread bearing support is installed.
Since it is always desirable for the rolling assembly so formed to be as light as possible, it is particularly advantageous to provide the mounting rim at the same time with a circumferential groove located on the side of the seat having the smaller diameter, which divides the bearing surface of the bearing support into two distinct zones. The tread bearing support can have an axial width equal to the distance between the inside walls of the two tire beads, and is then arranged over the full width of the rim""s bearing surface. The said support can also have a smaller width, and is then arranged only over the zone of the bearing surface closest to the rim seat of larger diameter, as described in the application WO 01/08905. In the latter case the said support has a base provided on its radially inside surface with a protuberance which, during the mounting operation, lodges in a circumferential groove provided for the purpose in the rim""s bearing surface, the said groove being closer to the end of the support zone on the side of the seat having the smaller diameter than to the end of the said zone closer to the rim seat having the larger diameter. Whatever its axial width, the tread bearing support pushes the bead with larger diameter axially outwards during mounting, so that the said bead will automatically locate itself on its rim seat.
Better control of the mounting of the tire-support assembly is obtained thanks to the presence, axially between the internal end of the inside wall of the rib near the rim seat of larger diameter and the end of the rim""s bearing surface, of a circumferential groove of small size. When the tire bead of larger diameter is moving onto the rim, it can catch slightly in the said groove. The resistance offered to the push serves as a sign indicating that the said bead is in place, and the second resistance noted is the last because it is due to the axially external hump of the rim.